The relationship between diet and colon cancer is complex and the roles for fat, fiber and energy in its induction and/or promotion are undoubtedly related. It has been particularly difficult to sort out the role for fiber. In most studies, the test fiber was not characterized or analyzed. Comparisons among studies are also difficult because of inconsistencies among other diet ingredients. The research proposed in this application will compare the physical properties, chemical compositions and biological effects of three different sources of dietary fiber. Constant daily diets will be used to control for most dietary variables that have made it difficult to determine fiber's role. Two, wheat bran and oat bran, have been selected because each is relatively homogeneous; yet, they have distinct physiological effects and are representative of naturally occurring sources of fiber in the food supply. Based on the recent recommendation that fiber be increased in the diet through the use of whole foods, not concentrates, the third fiber source will be that provided by a mixture of whole foods from all 3 classes of fiber-containing foods. The physical properties of each fiber will be determined by measuring bile acid binding, cation exchange and water holding capacities and particle size in vitro. Soluble and insoluble fractions of each fiber will be analyzed for individual pentoses and hexoses by HPLC, uronic acids, beta-glucans and lignin content. Biological responses have been selected on the basis of their potential to define the colonic environment and/or metabolic activity of colonic microflora and include: fecal neutral and acidic steroid concentrations, composition and solubility; microbial mass; fiber digestibility; stool weight; transit time; defecation frequency; fecal pH and redox potential. Determination of apparent absorption of selected nutrients will be an indirect indication of the substrate supply entering the colon and calcium balance will assess the short-term safety of the test levels. This research will establish relationships of biological responses to dose, chemical composition and physical properties of representative fiber sources in healthy adults as a prerequisite to developing therapeutic uses for fiber. Results from the proposed research will form justification for subsequent studies using invasive techniques.